Thrust block

Early thrust boxes

Early screw-propelled steamships used a thrust block or thrust box composed of perhaps a dozen lower-rated plain thrust journal bearings stacked on the same shaft.{{cite book

Although lignum vitae wood was used for the radial stave bearings in the stuffing box, cooled directly by seawater itself, this material wasn't capable of withstanding the force needed for the thrust blocks of any but the earliest screw vessels.

Each horseshoe was independently adjustable forwards and back, by either wedged gibs or a screwed adjustment. A particular problem with these thrust boxes was in adjusting them so that the force was shared equally between all the collars. Adjustment was often done on the basis of their operating temperature, gauged with the engineer's hand.

Improved Michell thrust blocks

Improved understanding of the theory of lubrication films (initially by Reynolds) allowed the development of much more efficient bearing surfaces. This allowed the replacement of multiple collars in a thrust box by a single thrust block.

In 1905, Australian engineer George Michell{{cite Australian Dictionary of Biography |title=Michell, Anthony George Maldon

Michell bearings contain a number of sector-shaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedge-shaped films of oil between the pads and a rotating disk on the shaft. Each lubricant "wedge" can only be of a limited length (in the direction of travel, i.e. circumferential) so multiple pads are needed rather than a single ring. No lubrication pump is needed: the rotation of the shaft itself is sufficient.

The need for an efficient thrust block became even more important with the advent of steam turbines, with their higher propeller speeds. Despite this, there was some reluctance to adopt them in their homeland, until the discovery that World War I U-boats were using them.{{cite episode

Michell Bearings continue in production today under the same name,{{cite web |title=Company history |publisher=Michell Bearings

References

References

1. "Kingsbury, Inc.".
2. "Thrust bearing".